The present invention is generally related to the field of heating devices, such as furnaces, water heaters, boilers, and the like. In particular, the present invention relates to a device for the control of draft in the flue stack of a heating device.
In order for a heating device to operate at its optimal level, the pressure across the heating device must be optimal. This is accomplished by creating enough energy in the heating device""s combustion chamber to allow some excess energy to escape out the flue stack of the heating device. The escape of the excess energy in the form of heated flue gas creates a draft out of the combustion chamber, up the flue stack, and out into the atmosphere. The draft allows the introduction of fresh air containing oxygen that fuels the combustion in the furnace.
However, if a high negative pressure occurs in the stack, the heating device will lose too much energy to the atmosphere and is, therefore, unable to create heat efficiently. This condition is typically caused by having a flue stack that is too large in height or in diameter for the combustion chamber.
For example, oftentimes when a heating device is replaced, a large combustion chamber is replaced by a smaller one, but the size of the flue stack is not changed. The size of the stack will be too large and will draw too much energy into the atmosphere, thereby creating an unsuitable environment for efficient heat production.
Alternatively, wind outside the flue stack may cause an additional draft which produces an excessive negative pressure. This condition is also not conducive to the production of heat in the heating device because the negative draft will draw too much air through the combustion process, thereby reducing the combustion temperature and reducing the efficiency of the heating device.
Several specific types of draft diverters and controllers have been developed to control the draft within the flue stack of a heating device. The simplest system of controlling the draft of a heating device is called a draft diverter. A draft diverter provides a means for allowing ambient air from the room, in which a heating device is located, to bypass the combustion process and thereby relieve the pressure across the combustion chamber.
Typically, an aperture is placed in the side of the flue which allows room temperature air from outside the flue to enter the flue pipe and be exhausted into the atmosphere instead of the heated air from within the combustion chamber, when a strong negative pressure is present. Additionally, heated air from the heating device is able to enter the room surrounding the heating device, thereby relieving pressure from the flue in cases of excessive positive pressure conditions.
In the case of negative pressure situations, the ambient air from the room surrounding the heating device may also be pulled through the draft diverter, up the flue stack and out into the atmosphere, thereby losing valuable heated air without providing a substantial benefit to the heating device. The problem with these systems is that they cannot be controlled and are, therefore, inefficient with regard to heated air being drawn out of the flue pipe space in order to prevent excess air being drawn through the heating device. The combustion chamber runs more efficiently, but the system as a whole does not run efficiently because the energy used to heat the room air when the room air is relieved through in the draft diverter. Also the pressure controlling ability of the device is limited to low pressures, because at higher pressures the diverter draws excessive amounts of warm room air through the draft diverter.
Another apparatus used to regulate the draft in a flue is a barometric damper. This apparatus works similar to the draft diverter. The barometric damper provides a cover over the open bypass hole in the flue. The cover is designed to open when the pressure in the flue exceeds the pressure limits of the combustion chamber. This saves energy as compared to the draft diverter because heated air from the space is not exhausted until a certain negative pressure has been reached. The device does not provide protection against high negative pressure because it acts like a draft diverter once the damper is open. This means that heated gas from the combustion chamber is drawn out of the stack instead. The barometric damper is a mechanical apparatus that responds to the change in pressure within the flue stack. The apparatus only responds to drastic changes in pressure and thereby does not keep the combustion chamber operating optimally, but merely relieves excessive pressure in order to keep the chamber operational.
The most sophisticated draft controller is an automatic draft control damper. The automatic damper is located within the flue and is generally designed having a flap that closes across the area of the flue stack. This damper has a better ability to control negative pressure than the barometric damper because the automatic damper modulates, through the use of an electric motor, to restrict the flow of flue gas leaving the heating device. The pressure drop across the damper counteracts the negative stack pressure resulting in a proper pressure across the heating device.
The automatic damper does not utilize an open bypass and thereby also saves energy due the fact that it does not draw any heated air out of the room surrounding the heating device. The problem with the automatic damper is that, due to its complexity and electronic control system, it is expensive, typically costing 10 times the cost of a barometric damper.
Accordingly, a device should be designed to restrict the size of the flue stack when negative pressure is present and allow a regulated flow of flue gases when positive pressure exists. The device should also be able to modulate to counter any negative pressure in the stack to maintain a set pressure at the heating device exit. Furthermore, the device should have a simple construction and be inexpensive to manufacture and maintain.
The present invention addresses these needs, as well as other problems associated with existing devices for controlling draft within a flue stack.
The present invention is a mechanical draft controller. The draft controller is comprised of a draft controller portion, a means for pivoting the controller portion, and a means for counterbalancing the controller portion. The draft controller portion has a surface that is movable in a generally arcuate path with respect to a central axis, a second surface extending between the first surface and the central axis, and two side surfaces extending between the first surface and the central axis. The side surfaces are spaced apart and have the second surface oriented between the side surfaces. The design of the device allows it to pivot into and out of the flow of gas in the flue depending upon the pressure of the flue gas stream, thereby modulating the pressure by restricting the area within the flue stack.
The aforementioned benefits and other benefits of the invention will become clear from the following description by reference to the accompanying drawings.